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First trials of ‘rare-earth free’ PMG clear scale-up toward 12MW

Tests on 1MW rig in UK show ‘excellent correlation’ of generator performance with computer modelling, says developer

Maiden trials of a new-look direct-drive permanent magnetic generator (PMG) that could be scaled up for use on 25MW offshore wind turbines have returned “very encouraging” results at the Offshore Renewable Energy (ORE) Catapult test centre in Blyth, UK.

The PMG, developed by start-up GreenSpur, is a modular concept engineered around magnets made of ferrites – an iron-rich ceramic – rather than current range of go-to rare-earths, the market for which is expected to see supply-side shortfalls in the coming years due to growing competition with other industries.

Lead-off tests of a 250kW unit, supported by £1.25m ($1.55m) grant from government funding body Innovate UK, “showed an excellent correlation between expected results and the data generated so far”, according to the company, which plans to finish preliminary analysis by the fourth quarter.

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“The current generation of direct-drive generators used in today’s offshore wind farms rely on rare-earth magnets,” said Andrew Hine, GreenSpur’s commercial director.

“It is very likely that the competition for magnet supply from other fast-growing industries, including defence, computing and electric vehicles will significantly impact the supply of rare-earth magnets to the offshore wind sector [and so drive up the cost].”

Preliminary tests of a ‘single-stage’ version of the generator on Catapult's 1MW drive-train rig were run at five and 10 revolutions per minute in ‘on-load’ and ‘off-load’ modes to check the mechanical and electrical performance of the concept.

Alex Freeman, operations director at GreenSpur, told Recharge: “The significance of these tests is articulated in the fact that there a strong correlation between the results we have so far and our modelling so this establishes confidence in the predicted performance of larger systems. We are very encouraged.”

GreenSpur is now moving forward with modelling for “significantly bigger, multi-megawatt generators”, with the target of designing a 12MW-plus concept for offshore turbine created by “stacking” three 4MW units in parallel.

Replacing high-price rare-earth materials with ferrites – a waste material produced in steel-making – would cut the cost of PMG magnets from £40 ($50) a kilogram (kg) to around £1/kg, according to GreenSpur calculations, meaning the design could carve around 33% out of the capital cost of direct-drive generator, and so almost 5% off the price of a turbine.

ORE Catapult ’s test facilities director, Tony Quinn, who also oversaw testing of a 75kW version of GreenSpur’s PMG in 2017, said: “This is a fantastic innovation, and a great example of a UK SME working with [us] to develop new technologies.”

Discussions with a number of OEMs to use the PMG in ultra-large-scale turbine concepts are “ongoing”, Freeman confirmed. The company foresees having a market-ready design by 2022.

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